During the first use, the unit smelled as if something electrical was burning. That burnt insulation smell. It lasted for about an hour then went away. I took 4 hours to make one gallon. Making my #2 gallon of water now & at 3/4 full, I estimate it will also be 4 hours for one gallon. Unit states 3 hours per gallon. Water tasted fine using the charcoal packet. I estimate it will take about 60 gallons for the unit to pay for itself. So far so good. But it's only been 2 gallons.